During the drilling, completion or work over of a subterranean well, it is frequently necessary to isolate one or more zones or sections of the well for various purposes. A permanent or retrievable well plug, such as a packer, bridge plug, tubing hanger assembly, positive-sealing-plugs or the like, will include an elastomer member for sealing across an interior area in tubular member or other well bore tubular previously set within the well. The elastomer member of such devices is expandable from a retracted position during run-in through the casing or opens whole on a conduit member, such as tubing, wire line or electric line, and is activated to seal within the well bore or tubular member through expansion.
The elastomeric member of the well plug may be a series of rubber-like solid seal elements which are squeezed or compressed into sealing engagement with the well tubular member by a compressive force generated or transmitted through the well tool.
After the compressive force has been applied for considerable time through such elastomer, anelastic behavior through the elastomer may occur. The industry widely uses cement retainers as a response to this behavior. Some such well plugs require up to 16,000 lbs. of force, or more, directed through the device to impart a compressive stress in the elastomer which causes it to form the necessary hydraulic seal in the well. During the application of such high compressive forces, such elastomers are less likely to remain static, but ooze and squeeze or otherwise result in an anelastic (time-dependent deformation) behavior which can be referred to as creep and stress-relaxation, whilst the third stage of creep has an accelerating creep rate and terminates by failure of material at time for rupture. The anelastic behavior of materials are amplified by conditions of increased temperature, changing temperature, increased pressure, saturation of water, water invading seal elements and/or invading gases.